According to the chart, 26.1million DS systems have been purchased in Japan, or 20.5% of the population of the country. That means that if each DS belonged to one person, one fifth of Japan would own a DS. Of course, each DS doesn't belong to one person -- people who bought DS Phats re-bought Lites and then DSis; and no doubt many people bought second systems for a new color scheme or a limited-edition, or to replace a broken system. Regardless, the DS has undeniably made its mark on Japanese society.
The US and Europe, on the other hand, have almost reached ten percent market penetration each. Just ten percent? That's merely outstanding -- what a disappointment for Nintendo.